Disk drives comprise a disk and a head connected to a distal end of an actuator arm which is rotated about a pivot by a voice coil motor (VCM) to position the head radially over the disk. The disk comprises a plurality of radially spaced, concentric tracks for recording user data sectors and servo sectors. The servo sectors comprise head positioning information (e.g., a track address) which is read by the head and processed by a servo control system to control the actuator arm as it seeks from track to track.
Data is typically recorded onto the disk surface by modulating a write current of an inductive write coil to generate a recording flux that magnetizes the magnetic medium to saturation. In longitudinal magnetic recording, the magnetic flux magnetizes the magnetic medium in an in-plane orientation (left or right) with respect to the disk surface, and in perpendicular magnetic recording, the magnetic flux magnetizes the magnetic medium in a perpendicular orientation (up or down) with respect to the disk surface. Disk drives may employ a Non Return to Zero (NRZ) modulation scheme wherein a “1” bit is recorded with a positive recording flux, and a “0” bit is recorded with a negative recording flux (or vise versa). During a read operation, a read element (e.g., a magnetoresistive element) senses the magnetic field emanating from the disk surface generated by the recorded data. The resulting read signal can be regarded as a superposition of the isolated transition responses at the linear bit positions.